Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2000
Abstract
No abstract has been registered
1999
Authors
Gro HylenAbstract
Age trends of phenotypic, environmental, and additive genetic variance and heritability were estimated for overall density and its components earlywood and latewood densities and latewood proportion. The objective was to acquire information for both individual and cumulated rings from ring number 3 to 12 counted from the pith. Age-age correlations were calculated for cumulated density traits only. The wood density data were obtained with X-ray analysis of increment cores from 47 open-pollinated families of Norway spruce (Picea abies (L.) Karst.). The families had earlywood and latewood with significant differences in density for individual and cumulated rings and consequently for overall density. The latewood proportion had significant family variation for cumulated rings but not for all individual rings. Large fluctuations in environmental variance caused fluctuations in heritability estimates for successive rings. A strong decrease in environmental variance for all cumulated traits, especially from ring 3 to 5, resulted in a steady increase in heritability estimates. The latewood density had the highest heritability estimates and latewood proportion the lowest for both individual and cumulated rings. Overall density and the cumulated components at cambial age 12 showed strong genetic correlations with their respective traits at all younger ages.
Authors
Svein SolbergAbstract
Relationships within stands between growth and crown condition are presented. The data set contained about 25000 trees on 500 plots. Growth of single trees was determined by diameter measurements in 1991 and 1996. Diameter increments were recalculated to relative values in two steps; firstly relative to their stem diameter, and secondly relative to reference values for trees in the same plot, having no defoliation or no discoloration. These relative increment values, or growth indices, were distributed on a scale common for all plots, rendering them influenced neither by site and stand properties, nor by social status of each tree. The correlation between crown condition and growth, although of moderate strength, did validate crown condition assessments as a meaningful, but rough measure of forest health or vigour. The relationships were concave, and considerable growth depressions were already found at slight levels of defoliation and discoloration. Growth approached zero as defoliation and discoloration increased towards 100%. These relationships applied for all plots, regardless of their site productivity, development stage or regeneration method
Abstract
This study describes how crown density changes were distributed within monitoring plots, in order to determine whether the reduced crown density observed could be explained as a worsening of a limited number of unhealthy or small and slightly suppressed trees.Crown density, yellowing, coning and stem diameter data were available from 447 selected plots comprising 22560 single trees all having a complete 1990-97 series of crown condition data.The eight years series of crown density for each tree were recalculated to two median values, for 1990-93 and 1994-97, in order to reduce the influence from short time variations including random errors. The scores for yellowing and amounts of cones were averaged over the years 1990-93. These variables, and diameter, were recalculated to rank indices within each plot.Relationships between variables were described by graphs and examined by correlation analyses of the indices. The trees tended to retain their internal ranking. Generally, when crown density for a plot has changed, most of the trees were affected. The most defoliated trees in each plots had the least negative changes, but except from that the trees were equally affected regardless of their yellowing, amount of cones, and their size.The results demonstrates that any effects from competition between the trees were sufficiently removed in the assessments, even in densely stocked stands.
Academic – Crown density assessments, control surveys and reproducibility
Svein Solberg, Lars Strand
Abstract
This study aims to evaluate the quality of crown density data, based on independent, pairwise tree assessments. The data originates from monitoring of forest health (crown condition) in Norway; 250 plots, comprising 12 000 individual trees of Norway spruc e, have been reassessed by a single observer during 1990-95. Of the trees, 2300 were controlled more than twice, providing the possibility of evaluating the quality of assessed temporal changes of crown density. True errors (standard deviation) are estima ted to be about 10% for single trees and 5% for plot means, while the real standard deviation of the differences were slightly higher. The errors of the temporal changes of crown density were of similar magnitude. Systematic differences in crown density w ere found between sites and plot types, partly resulting from observer bias. However, the results suggest that observer bias is really the result of each observer\"s personal style in assessment.
Authors
Svein SolbergAbstract
On the local county monitoring plots located throughout Norway a reduction of crown density has been noted during 1988-97. The aim of this study was to determine whether this change could be attributed to normal effects from increased age on the plots.The dataset comprised around 580 plots and 27 000 single trees of Norway spruce, where each tree was provided with ten years of crown density measures. A two step approach was used, firstly to search for an expectancy for normal reduction of crown density by age derived from the dataset, and then to compare this with the actual reduction. The interpretation was somewhat complicated as the various results were tangled into each other.Highly significant correlations were found between crown density and age. The relationship indicated an annual reduction of crown density around 0.12%-units, however, the relationship varied both between years and between regions, and it was not possible to definitely determine whether the relationship was best described by linear or non-linear models.Of major importance here is that the relationship appeared to be influenced by the presence of stresses, which effects tended to be more severe in old stands. Based on this it seems questionable whether an expectancy for normal ageing can be properly defined. However, in the present study it could still be definitely determined that the mean crown density change of -0.41%-units annually was too negative to be attributed to normal ageing, as it was clearly below all the suggested expectancies from the various models.This suggests that the amount of stress in the period under study has been higher than normal, and this encourages the search for causal agents in further studies. Changes in silviculture may have had some influence.The results were valid for most of Norway, with the exception of western and northern regions. Crown density assessments are subjective, which may possibly give erroneous time trends, however, it is argued that this is less likely to be of major importance in the present data.
Authors
Svein SolbergAbstract
No abstract has been registered
1998
Abstract
Concentrations of pigments in needles of yellowish Norway spruce (Picea abies (L.) Karst.) trees suffering from either N, Mg or K deficiency in field sites in southeast Norway are reported. The yellowish trees had a considerably lower (roughly 50%) pigment concentration, as well as a lower chlorophyll/carotenoid ratio, compared to the green trees within the same sites. Yellowing was interpreted as a general bleaching of colour, as well as a slight turn from the green (chlorophylls) towards yellow (lutein). Concentrations of pigments were highly intercorrelated. N deficiency was especially associated with low a-carotene concentrations. This was interpreted as a-carotene being the most sensitive pigment to stress. However, this pigment might be specifically sensitive to N deficiency. Carbohydrate concentrations were slightly higher in yellowish trees.
Authors
Aksel GranhusAbstract
No abstract has been registered
1997
Authors
Svein SolbergAbstract
No abstract has been registered